RF Spectrum - The same RF spectrum of 2 - 30 MHz used in the Manchester, UK trials by NOR.WEB still forms the basis for solutions in 2002.
Modulation techniques are now much better understood. Multi-frequency carrier technology, such as OFDM is in use, but some spread spectrum approaches have alsobeen tried successfully. A number of vendors are still secretive about their favoured modulation scheme.
Design of a Powerline interface - The technology has differentiated the design of a Powerline interface in a layered fashion. The physical layer and the Media Access (MAC) layer are implemented in Powerline chip sets. The Powerline channel is a difficult and variable environment, so the MAC layer must implement the dynamic measurements necessary to adapt the transmission requirements of the communications channel to the Powerline channel. The actual communication services are then designed to live on top of the MAC layer.
Food chain - Powerline chipset vendors have emerged and Powerline system integrators package those chipsets into product. Few “monolith” companies still exist, such as Ascom who have their own chipsets and also do systems integration.
Initially, the applications split into in-house and access systems.
The HomePlug Alliance in the United States led efforts to come up with good, standardised in-house solutions. In July 2001, the HomePlug Specification 1.0 was ready and is endorsed by about 30 vendor companies.
Europe continued to concentrate on access systems, driven by thePLCforum. There is evidence however, that this split may become less meaningful as time goes on.
Early on, the two dominant access system vendors, Siemens and Ascom, had determined that they could not hope to sell access system solutions without also offering compatible in-house product.
Unexpectedly, Siemens withdrew from the Powerline market and ceased all Powerline activities just before the CeBIT 2001, the major fair for the Powerline industry.
Also unexpectedly, Oneline, Germany, announced the halting of the development of Powerline-Communications stating that “Altered environment renders operations economically unviable for foreseeable future”. (www.oneline.de)
Oneline states that “government regulations on the emission of electromagnetic waves were an important factor in its decision. The mandated limits are extremely low. Moreover, the government intends to prohibit certain special frequencies. In this context, it would take at least two more years of development before Powerline Communications would be ready for the mass consumer market”
Today, Main.net has developed such a powerful Powerline system product (based on Itran chipsets) that they claim their product can be used equally well for access as it can be used for in-house systems.
With adaptive modulation level mechanisms, transmission through electric meters and even transformers became feasible. By adjusting the modulation power, they can even “reuse” the frequency spectrum in some cases.
While HomePlug concentrated on the in-house market, their chip sets are designed to be also usable for access purposes later on. Using sophisticated modulation schemes a throughput of perhaps 15 Mb/s can be readily achieved using the frequency spectrum of 5-22 MHz with the modulation power still within the limits of FCC Part 15 rules, covering the majority of typical in-house applications in the US.
A weakness of this technology for access is that the limited information throughput of, currently, about 2 Mb/s is shared by all customers on a substation transformer, which will surely lead to inadequate bandwidth for some customers. Forrester Research has recently pointed that out as a severe weakness, markedly considering the competition of the emerging DSL services.